Thus, for any compound system, almost all states are entangled, as the non-entangled ones are vanishly small (measure zero) subset of all possible states. For example, any time you measure a particle with apparatus, after measurement the apparatus indicates something about the measured system.

Are particles naturally entangled?

A single particle can even be entangled with the vacuum state, for instance, a single photon incident on a beamsplitter. ... The simple consequence is that natural systems are and behave as entanglement requires. Without entanglement the complex atoms will have completely different properties.

Is every particle quantum entangled?

In fact, a typical particle is entangled with many particles far outside our horizon. ... When two particles interact, their quantum states gen- erally become entangled. Further interaction with other particles spreads the entanglement far and wide.